They would give you whatever they give you. I haven;t had too much of a problem with them as I say, but on the odd occasions I have, would just phone up and say that the *whatever* was well on the turn and I would NEVER have picked it for myself etc...and they refund you the cost...but I think if anything they're getting better and better about this (probably because if their policy IS to refund for online deliveries, they're potentially better off getting their shoppers to pick half decent stuff).
I have had more problems with bread being very close to the sell by date, but again, not often.
Also Tesco clubcard points can be saved and redeemed at 4x their face value on a variety of holidays etc (gonna go youth hostelling with mine, for a quarter of the usual price!

).
If you do want to collect those to use against their clubcard deals, you're often better off looking for vouchers giving extra points, instead of a cash value.
Does that all make sense?